1. Field of the Invention
The present invention relates to a method of removing coronene deposits from a heat exchange zone of a reforming process.
2. Description of the Prior Art
Reforming is a well-known process in which a hydrocarbonaceous feedstock, such as naphtha, is contacted at elevated temperature and pressure in the presence of added hydrogen with the solid catalyst to increase the aromaticity of the feedstock. See, for example, Hydrocarbon Processing, Sept. 176, pp. 171-178. The effluent of the reforming zone comprises undesired polycyclic aromatic compounds, including coronene, in amounts which vary depending on the operating conditions. Coronene (C.sub.24 H.sub.12) is a polycyclic aromatic compound having a structure which contains 7benzene rings in a circular pattern with no side chains. Its molecular weight is 300 and its melting point is 440.degree. C. Because of its high melting point, when coronene is present in relatively high concentrations, coronene readily deposits as a solid upstream of the effluent dew point in the heat exchanger used to cool the effluent.
U.S. Pat. No. 3,322,842 discloses recycling a portion of the gasoline reformate to the total reaction effluent prior to separating the reaction product into gaseous phase and liquid phase to minimize catalyst deactivation caused by polycyclic aromatic compounds such as coronene.
U.S. Pat. No. 1,672,801 discloses the use of solvent, such as naphtha, to dissolve asphalt in clogged draw-off pipes or separation zones of hydrocarbon conversion processes.
U.S. Pat. No. 3,725,247 discloses that polynuclear aromatics which have a deleterious effect on the catalysts are formed during hydrocracking. It teaches treatment of the catalyst to avoid formation of polyaromatic compounds.
U.S. Pat. No 2,953,514 relates to a method for reducing heat exchanger fouling. It discloses injecting a portion of the liquid reformate boiling at least about 450.degree. F. in the stream of the reactor effluent at a point upstream of the heat exchanger.
It has now been found that in a reforming process wherein the reforming zone effluent is passed into two parallel trains of heat exchangers, by reducing the flow of reforming zone effluent in one of the trains of heat exchanger to a temperature sufficient to condense at least a portion of the reformate therein while increasing the flow in the other train of heat exchanger, the coronene deposition can be removed from the first train of heat exchangers.